Field
This invention relates generally to an antenna subsystem for a communications satellite and, more particularly, to a cross-link antenna for satellite-to-satellite communications in a constellation, where the cross-link antenna comprises eight quadrifilar helices situated in a ring around an L-band satellite-to-earth antenna, and the quadrifilar helices have a smaller and more effective design which improves both satellite-to-satellite and satellite-to-earth communications performance.
Discussion
Communications satellites are used to enable many different types of telecommunications. For fixed (point-to-point) services, communications satellites provide a microwave radio relay technology which is complementary to that of communication cables. Communications satellites are also used for mobile applications such as communications to ships, vehicles, planes and hand-held terminals, global positioning system (GPS), and for TV and radio broadcasting.
In one common implementation, many communications satellites are placed in low earth orbit (LEO) or medium earth orbit (MEO) in a constellation which circles the earth. The individual satellites in the constellation communicate with each other, and also communicate with users and communications providers on or near the earth's surface. The communications among the satellites in the constellation are handled by what are known as inter-satellite links (ISL) or cross-links.
Some satellite constellations use reflector-type antennas for ISL or cross-link, however these types of antennas and their control systems are expensive and bulky. It is desirable, where possible, to use simpler antennas for cross-link communications. However, the cross-link antennas must not only be effective in satellite-to-satellite communications performance, but must also not be detrimental to satellite-to-earth communications performance. These requirements have been difficult if not impossible to meet using past cross-link antenna designs.